Various support and positioning structures are known for use in microlithographic instruments. Typically, in the prior art, XY guides, including a separate X guide assembly and Y guide assembly, are utilized with one guide assembly mounted on and movable with the other guide assembly. Often, a separate wafer stage is mounted on top of these guide assemblies. These structures require high precision and many parts. Typically, external forces directed to parts of the positioning assembly and reaction forces due to movement of different parts of the assembly are coupled directly to the image forming optics and reticle handling equipment resulting in unwanted vibration.
U.S. Pat. No. 5,120,036 to Van Engelen et al. describes a two-step positioning device using Lorentz forces and a static gas bearing for an opto-lithographic device.
U.S. Pat. No. 4,952,858 is directed to a microlithographic apparatus utilizing electro-magnetic alignment apparatus including a monolithic stage, a sub-stage and isolated reference structure in which force actuators imposed between the monolithic stage and the sub-stage are used for suspending and positioning monolithic stage in space. In this apparatus a Y frame or stage is mounted on an X frame and the monolithic stage is positioned from and supported in space from the Y frame.